A circus owner walked into a bar to see everyone crowded about a table watching a little show. On the table was an upside-down pot and a duck tap-dancing on it.
The circus owner was so impressed that he offered to buy the duck from its owner. After some wheeling and dealing they settled for $10,000 for the duck and the pot.

Three days later the circus owner runs back to the bar in anger, "Your duck is a rip-off! I put him on the pot before a whole audience and he didn't dance a single step!"

"Well," said the duck's former owner, "did you remember to light a candle under the pot?"